Soft ear inserts are part of sound devices which are often worn for significant periods of time during the day. Today, these devices include hearing aids, personal sound amplifiers (PSAP's), Bluetooth Headsets and Audio Headsets, to name a few. These soft ear inserts and associated devices are referred to herein as “ear tips.” For these products, early technology used soft urethanes and foams which often discolored or quickly dirtied needing frequent replacement and were rigid enough to cause significant ear discomfort over extended periods of daily usage. The industry has since moved to mostly silicone ear tips which provide a softer material for increased comfort and biocompatibility. Silicone ear tips have also the additional advantage of mechanical elasticity memory. That is, they maintain their grasping force once mounted onto the sound port nozzle.
Silicone based ear tips or ear inserts, widely used today, are biocompatible and can be adjusted to the proper level of softness for the desired comfort. Ear tips used by devices without ear level microphones such as headphones, provide comfort and isolation of the ear canal from ambient sounds. Many times the ambient sounds are not sufficiently attenuated inside the ear canal which can be caused by the ambient sound pressure vibrating the ear insert and deforming the surfaces of the ear insert exposed to and in direct response to the air pressure modulation of said ambient sound field. This deformation propagates through the body of the ear insert which in turn causes deformation of the ear insert on its other surfaces which face the occluded ear canal space. This causes a related sound pressure to be developed inside the ear canal cavity. This effect is especially apparent if the insert is made of thin silicone. The action of the surfaces is similar to the walls of a balloon expanding and contracting in response to changes of the air pressure within. This effect represents the conversion of acoustic energy to mechanical vibrational energy and back to acoustic energy. This unintentional and undesired acoustic to mechanical and back to acoustic (acousto-mechanical) sound coupling is referred to herein as the “ballooning effect.” In order to increase the acoustic seal and reduce vibration and the “ballooning effect” of the ear insert and thus increase the attenuation of external ambient sound, the ear inserts need to be made of thicker or harder silicone thus compromising comfort.
For devices that provide high amplification and have ear level microphones, the ear insert should also provide sufficient sound seal as to limit “sound leakage” from inside the ear canal cavity to outside where the microphone is in order to avoid well known feedback. A sound containing or transmission body such as an ear tip or ear insert or a sound tube consists of a body made of a deformable solid material and having first surfaces (or first walls) in contact with a first air path which in turn contains an intended sound pressure (said first air path also referred to as a sound containing or sound transmission path). Second surfaces (or second walls) of the sound containing body may be in contact with other air paths or with free air but are distinguished from first surfaces as not being in direct contact with said first air path. “Sound leakage” is not necessarily due to the obvious failure of an incomplete air-tight seal to close off an unintentional air path or leak from the first air path but also through the same non-obvious mechanism referred to above as the “ballooning effect” wherein said intended sound pressure contained within the first air path expands and contracts the first surfaces or first walls and wherein the expansion and contraction of said first walls or first surfaces causes related deformation of second surfaces or walls which then in turn re-radiates an unacceptable portion of the intended sound pressure as a corresponding unintended sound pressure into said other air paths or to free air. Thus the leakage could be in the form of direct sound pressure leakage due to insufficient air-tight seal or in the form of sound pressure generated by the vibration of the soft walls of ear insert due to the “ballooning effect” from sound pressure delivered to the ear canal enclosed by the ear tip.
Newer, highly elastic yet vibration and sound damping materials have now become available which when used to manufacture an ear tip improve comfort during prolonged headset ear tip usage as well as significantly decrease said “ballooning effect” both to and from the human ear canal. These materials do so by converting less of the mechanical energy imparted by the contained acoustic pressure into expansion and contraction of the walls, while more of said mechanical energy is dissipated as heat within the material due to its internal damping characteristics. Note that damping used to ameliorate the “ballooning effect” should in no way be confused with any unrelated damping of the air path used as a sound passage by placing acoustic resistances in the air path. Any further references to sound damping herein specifically refer to internal vibrational damping of the material making up the walls or surfaces of said sound containing or sound transmission body for containing, isolating or delivering a sound pressure rather than damping the air path of a sound transmission body. The drawback to these types of highly elastic and sound vibration damping materials is that they are so soft and elastic that when they are mounted onto a sound port nozzle of an amplification device they do not have robust mechanical retention. These materials have low elasticity memory and when installed onto a device they often stretch, expand, and remain in this steady state expanded condition. In this condition, the materials by themselves do not provide enough residual retention to remain on the nozzle when being removed from the human ear. This inadequate retention results in the ear insert falling off or remaining stuck in a human ear leaving the user to attempt to remove it, or worse, make a trip to an emergency room or doctor to remove the ear tip. These situations range from a major annoyance to the consumer to more dangerous medical outcomes and increased liability for companies selling these devices.
Low retention forces of ear inserts to amplification devices/headsets (usually those lower than 200-300 grams) often have outcomes of an eventual failure of an ear insert to remain mounted onto a headset. Although this retention force number is dependent on many variables including the base materials of the headset and ear tips, ear wax, body oils, cleanliness of the interface, and geometries of the ear tip, the mating portion of the headset and the human ear canal being entered, the fact remains, at these low forces, potential ear tip mechanical retention failures can and do occur. Higher retention forces of ear tips to headsets (usually those over 1000 g) provide a reliable mechanical retention of the ear tip to the headset supporting any combination of variables described above as well as keeping the force low enough for a user to easily assemble an ear tip on their headset.
It is not intended to specifically define herein all current and future materials that fall into the category described as “highly elastic, sound and vibration damping” materials which reduce the “ballooning effect”. One such material available today is Qflex made by Flexan Corp. Silicone, by contrast, has far less vibration and sound damping capability.
In view of the foregoing, there is a need for an alternative means for creating mechanical retention to allow technically superior, highly elastic, sound and vibration dampening acoustic ear tip materials to maintain proper retention on associated headset devices.